Technical Field
The present disclosure relates to an efficient and scalable method for producing graphene of controllable thickness and purity via intercalation of graphite with dicarboxylic acids of various molecular chain lengths and exfoliation.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Graphene is a two-dimensional crystalline material which is a monolayer of the material graphite with thickness of approximately 0.30-0.35 nm [Nobelprize.org. The 2010 Nobel Prize in Physics: Press Release; 19 Oct. 2010. http://nobel prize.org/nobelprizes/physics/laureates/2010/press.htm.—incorporated herein by reference in its entirety]. Thin graphite flakes consist of several layers of carbon atoms, including monolayer graphene. This graphene may consist of an isolated single layer of a hexagonal carbon network which is composed of sp2-hybridized C—C bonding with π-electron clouds [Y Ohashi, T Koizumi, T Yoshikawa, et al. TANSO 1997; No. 180: 235-8.—incorporated herein by reference in its entirety]. The strong G bonds formed among the sp2 hybrid orbitals in graphene result in an exceptionally high breaking strength and modulus of elasticity. Moreover, the π and π* bonds formed through the hybridization of the Pz atomic orbitals of the nearest carbon atoms cause an extraordinarily high conductivity [Y Ohashi, T Hironaka, T Kubo, et al. TANSO 2000; No. 195: 410-3—incorporated herein by reference in its entirety].
Due to the unique physical properties of graphene, including high stiffness, high carrier mobility, unusual magnetic properties and the room temperature quantum Hall effect, graphene has been employed in diverse technological applications such as biosensors, super capacitors and hydrogen storage materials. Therefore, it is important to develop rapid, easy and affordable methods to prepare high quality single layer graphene nanosheets free of defects.
Since the Nobel Prize in physics in 2010 was awarded to Professors A. Geim and K. Novoselov for their experiments on graphene, great efforts have been employed to prepare graphene [K S Novoselov, A K Geim, S V Morozov, et al. Science 2004; 306:666-9.—incorporated herein by reference in its entirety]. A variety of synthetic methods to prepare graphene have been developed which include mechanical cleavage of graphite, chemical vapor depositions (CVD) on different metal substrates, thermal decomposition of silicon carbide (SiC), chemical exfoliation of graphite and unzipping of carbon nanotubes via argon plasma etching.
The mechanical cleavage method was developed by A. Geim and K. Novoselov and involves introducing graphite powder to double-sided adhesive tapes and repeating the cleavage process several times until the graphite flakes become transparent with a thickness of approximately 15-110 nm. This method is not beneficial from a commercial or industrial standpoint. Additionally, the obtained thickness can be very large compared to the actual thickness of graphene (0.30-0.35 nm). The CVD techniques are based on the use of methane gas, hydrogen and argon in a thermal reactor at very high temperatures exceeding 1000° C. to form a graphene layer on a thin metal foil such as copper or nickel [Y Zhang, J P Small, W V Pontius, et al. Appl Phys Lett 2005; 86:073104; and J C Meyer, A K Geim, M I Katsnelson, et al. Nature 2007; 446:60-3.—each incorporated herein by reference in its entirety]. Although this method produces high quality graphene, it requires several tedious steps to transfer prepared graphene onto a silicon substrate to fabricate electronic devices. These steps include a spin coating of polymer on the metal foil that has graphene, followed by etching of the metal foil, transferring of the polymer coated graphene to a silicon/silicon dioxide (Si/SiO2) substrate, and decomposing the polymer by ozone etching to remove the polymer. Such CVD methods are very harsh and expensive from an economical point of view. The same disadvantages have been observed for thermal decomposition of silicon carbide and the unzipping of carbon nanotubes by argon plasma etching [J C Meyer, A K Geim, M I Katsnelson, et al. Solid State Commun 2007; 143:101-9.—incorporated herein by reference in its entirety].
In chemical exfoliation methods or “Hummar methods”, graphite is first treated with a mixture of sulfuric and nitric acids at low temperature followed by the addition of sodium nitrate and potassium permanganate and a gradual increase in the temperature up to 90° C. This method produces graphene oxide which consists of several layers rather than the desired monolayer. Furthermore, an additional step is required to reduce the graphene oxide to graphene [S Neubeck, Y M You, Z H Ni, et al. Appl Phys Lett 2010; 97:053110; and C H Lui, L Liu, K F Mak, et al. Nature 2009; 462:339-41.—each incorporated herein by reference in its entirety].
In view of the forgoing, one object of the present disclosure is to provide a simple, low cost, and efficient method to economically produce graphene on a mass production scale of a quality for industrial use. A further aim of the present disclosure, is to provide a method where the desired thickness and number of layers of graphene can be controlled during production, including monolayer graphene, bilayer graphene, and/or multilayer graphene by intercalating graphite with dicarboxylic acids of various molecular lengths and exfoliating to produce graphene.